`test_macro_properties` concurrency issue

[qRoC]

---- test_macro_properties stdout ----
thread 'test_macro_properties' panicked at fastrace/tests/lib.rs:758:5:
assertion `left == right` failed
  left: "\nroot []\n    bar_async []\n    foo_async [(\"k1\", \"v1\"), (\"a\", \"argument a is 1\"), (\"b\", \"Bar\"), (\"escaped1\", \"Bar{}\"), (\"escaped2\", \"{ \\\"a\\\": \\\"b\\\"}\")]\n"
 right: "\nroot []\n    bar []\n    bar_async []\n    foo [(\"k1\", \"v1\"), (\"a\", \"argument a is 1\"), (\"b\", \"Bar\"), (\"escaped1\", \"Bar{}\"), (\"escaped2\", \"{ \\\"a\\\": \\\"b\\\"}\")]\n    foo_async [(\"k1\", \"v1\"), (\"a\", \"argument a is 1\"), (\"b\", \"Bar\"), (\"escaped1\", \"Bar{}\"), (\"escaped2\", \"{ \\\"a\\\": \\\"b\\\"}\")]\n"
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[andylokandy]

Dulicated with #9